Utilization of low energy membranes operating at low pressure for treating wastewater is developed to reduce operational and maintenance costs of a water treatment system. Depending on the operating conditions of the water treatment system, the low energy membranes can remove contaminants including micro-pollutants, nano-sized anionic substances and metals.
As compared to a conventional cellulose acetate membrane, an aromatic polyamide membrane improves membrane technology by offering better rejection towards salts and water soluble organics, providing a better resistance against hydrolysis and biological attack, withstanding higher temperatures and operating over a wide pH range of 2-10.
The aromatic polyamide membrane has better salt rejection than cellulose acetate membrane due to lower diffusivity of NaCl but higher permeability, solubility and diffusivity of water across the aromatic polyamide membrane.
There are some prior arts relating to several membrane systems or methods for treating wastewater or saline water by reverse osmosis.
Japanese Patent No. 2007105572 claims a water purification system where raw water is filtered by a reverse osmotic membrane type filter means separating into permeate or purified water and retentate of non-transparent water. A water purification circulating route branches from an injector-pipe way pours the permeate into a reservoir and supplies water to the reverse osmotic membrane type filter means according to irrigation operation by a control means.
Another Japanese Patent No. 2001113136 discloses a reverse osmosis treatment device comprising a pump which raises raw water to a predetermined pressure for supplying to a reverse osmosis membrane module, a bypass passage which bypasses raw water provided in a discharge side of the pump and breathed out from the pump to the reverse osmosis membrane module, a flow control valve provided in the bypass passage to adjust a bypass rate of the raw water.
United States Patent No. 2007289904 describes a reverse osmosis system including a membrane chamber having a feed line to generate into a permeate stream and a brine stream, a booster device having a turbine portion in fluid communication with the brine stream and a pump portion in fluid communication with the feed line.
In the prior art, a method of operating the reverse osmosis system comprising pressurizing the feed line, generating a first flow signal corresponding to a flow of fluid in the permeate stream, operating a variable frequency drive in response to the first flow signal, controlling the motor in response to the variable frequency drive, generating a second flow signal corresponding to a flow of fluid in the brine system and controlling opening of a variable size nozzle coupled to the turbine portion in response to the second flow signal.
U.S. Pat. No. 6,162,361 claims a method for separating and recovering heavy metals from a wastewater stream comprising passing the wastewater stream through a plurality of nano-filtration membranes being arranged in a series or parallel arrangement providing a permeate and a concentrate output stream and passing the concentrate output stream through an electro dialysis device for additional concentration of heavy metal ions. The claimed method shall further comprising a step of passing the permeate output stream through a plurality of nano-filtration membranes arranged in a series or parallel arrangement.
Typical reverse osmosis membrane requires high operating pressure in water treatment systems. However, it is important to reduce the operational and maintenance costs of the system by utilizing a low energy membrane which can operate at low pressure but at the same time provide satisfactory performance for treating wastewater by removal of various pollutants in high amount.